Cool, just created a folder with audio files and now in im_chat I can hear the sound :)
But my question was not strictly related to im_chat. I've had in mind a sound notification about calendar events. So when you create some event in calendar I would like to hear the sound when notification is displayed on the screen.

I tested again the im_chat sound and is working, last time I used it was on an earlyer version of V8. Seems ok to me. But since you need to add sound (client side) for events/calendar you need to edit the js on calendar module.

SS*: all you have to do is just create a folder inside the im_chat module /im_chat/static/src/audio and add some audio files in mp3 or ogg format but remember to change audio file name to 'purr' or 'ting' or if you want to any other but some changes are required in js file /static/src/js/im_chat.js

So finally I have im_chat with audio notification which is very useful.